Question

plzzz help me out with these questions....

Answer 1

hey i know 20 question only.
(a+b+c)(a2+b2+c2-ab-bc-ca)
(a+b+c)(a2+b2+c2-(ab+bc+ca)
a2+b2+c2=83
(a+b+c)2=a2+b2+c2+2(ab+bc+ca)
(15)2=83+2(ab+bc+ca)
225-83=2(ab+bc+ca)
142/2=(ab+bc+ca)
71=(ab+bc+ca)